DEFINITION 1: Many systematic reviews contain meta-analyses. Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review (see Chapter 9, Section 9.1.3). They also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies.
Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from //training.cochrane.org/handbook
DEFINITION 2: A systematic review is an overview of primary studies that used explicit and reproducible methods. A meta-analysis is a mathematical synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way. Although meta-analysis can increase the precision of a result, it is important to ensure that the methods used for the review were valid and reliable.
Trisha Greenhalgh. How to read a paper: Papers that summarise other papers (systematic reviews and meta-analyses) BMJ 1997; 315: 672. Available here.